1. Field of the Invention
The present invention relates to an electronic timepiece including a solar panel.
2. Background Art
There is a digital electronic watch with solar cells in the related art (for example, see JP-UM-A-56-97795). The digital electronic watch with solar cells disclosed in JP-UM-A-56-97795 blocks display output from a driver circuit, when output of the solar cells is equal to or less than a predetermined value.
There is an electronic timepiece in the related art (for example, see JP-A-61-77788). A digital electronic watch with solar cells disclosed in JP-A-61-77788 stops a time point display operation when incident light is not continuously obtained for equal to or more than given time.
In an electronic timepiece including a solar panel, it was general to perform an illuminance detection operation of the solar panel every two seconds for improving responsiveness when returning from a power saving mode to a normal mode. However, in both cases of the normal mode and the power saving mode, if the illuminance detection is performed every two seconds, the generated energy of the solar panel is consumed during each illuminance detection and there was a limit on the improvement of the generating efficiency of the solar panel.
In addition, when a state where the generation of electric power is not performed by the solar panel is continued for a given time (for example, 30 minutes to several hours) is detected to transition the electronic timepiece to the power saving mode, in the given time, if the illuminance detection operation is performed every two seconds, electric power which is necessary for the illuminance detection operation is supplied from the secondary battery and the electricity consumption of the secondary battery increases by the same amount. Accordingly, there was also a limit on the improvement of the duration of the secondary battery in a case of the transition to the power saving mode.